You will enter only the amount that you individually paid for rent within tax year 2015.
Your roommates will do the same on their own tax returns, and you will all be able to claim the Michigan Homestead Property Tax credit. (Well, as long as each of you meet the the eligibility requirements as well)
It is not as if there is 1 renters credit per house rule. You are each individuals and you each pay your own amount of rent each month. Therefore, you will enter the amounts you paid for your portion of rent only, when filling out the MI homestead property tax credit questions.
